The present invention relates to power tools in general and more particularly to a power drill which is capable of working in a normal drilling and an impact drilling mode.
There are already known various types of impact drilling power tools in which a driving motor is accommodated in a power tool housing which further accommodates a driving arrangement or transmission that can be switched between a normal drilling mode and an impact drilling mode and which rotates a spindle element mounted in the housing. The axial movement of the spindle element when the power drill operates in an impact drilling mode results from an axial displacement of an impact element which impacts against the spindle element. Usually, the impact element becomes active only when the spindle element, which is acted upon by a force of at least one spring, is subjected to an axial force opposite to the force of the spring, whereby the power drill is switched from its normal drilling mode into the impact drilling mode.
In one of such conventional impact power drill constructions, a single or a multiple helical cam surface is formed at the outer circumferential surface of the impact element, and a number of axially extending depressions is provided which corresponds to the number of the cam surfaces. A corresponding number of rolling bodies is provided which are located radially outwardly of the outer circumferential surface of the impact element and cooperate with the cam surfaces and the depressions. The rolling bodies are constitutent parts of a cam follower element which further includes an outer race having an annular groove in which the rolling bodies are received, the outer race being stationarily mounted in the housing and thus preventing the rolling bodies from axial displacement. In this prior art device, the cam surface may be provided on radially extending helical projections, and the axial depressions may be constituted by interruptions, the rolling bodies contacting the outer circumferential surface of the impact element and, in the impact drilling mode, also the cam surfaces to thereby displace the impact element in the axial direction against the force exerted by a spring so that energy is stored in such spring until the rolling bodies are juxtaposed with the respective interruptions upon which the impact element is released for a rapid displacement in the axial direction under the influence of the spring to thereby subject the spindle element to an axial impact.
In one conventional power drill of this type, the impact element is of a sleeve-like configuration and is mounted on the spindle element for displacement axially of the latter. Experience with this construction has shown that the spindle element must have an excessive axial length in view of the fact that the spindle element must extend over the entire length of the housing. In addition thereto, the excessive length of the spindle element makes the entire power drill considerably long and thus renders handling of such power drill difficult.